The overall objective of the research program is to demonstrate and characterize the lymphoblast-associated antigens on the surface of normal lymphocytes transformed by continuous culture in vitro or following incubation with mitogens. The occurrence of these determinants on normal or leukemic lymphoblasts will be identified by their capacity to stimulate the proliferation of autologous lymphocytes and their reactivity with anti-lymphoblast antibodies. The expression of lymphoblast-associated antigens during specific stages (Gl, Sl, G2, M) of the cell cycle will be determined during lymphoblasts grown in continuous culture and blood lymphocytes stimulated to proliferate by plant mitogens. Whether these determinants appear on all lymphoblasts or only on lymphoblasts derived from B-lymphocytes will be determined. Finally, the biologic significance of the proliferative response of lymphocytes to autologous lymphoblasts in terms of the expression of an immunologic control mechanism will be investigated.